One part of the arterial system of blood-vessels runs to the stomach and intestines, and is distributed over their walls in fine divisions. These connect with the capillaries of the portal vein, which leads to the liver. During this passage of the blood from one system to the other, part of the digested food is taken up. Now it is very evident that the quantity of material thus absorbed must vary greatly at different times according to the nature and amount of food supply and the activity of the digestive processes. If, therefore, the blood from the alimentary canal was allowed to pass directly into the general circulation, the supply to the tissues of the nutrients, especially the carbohydrates, would be very uneven.

145. Function Of Liver

Just here comes in a liver function. In that organ there is found a starch-like body known as glycogen (see p. 73), which appears in increased quantity following the abundant absorption of sugar from the intestines. It is believed, because of this and other facts, that the liver acts as a regulator of the carbohydrate supply to the general tissues of the body, storing a temporary excess of the sugar in the form of glycogen, which is gradually given up to the general circulation as it is needed after first being transformed back to sugar. Glycogen is also stored in the muscles, in an amount equal to or greater than that in the liver.